1. Field of the Invention
This invention relates generally to extraction of hydrocarbon fuels from a body of fixed fossil fuels in subsurface formations such as oil shale, heavy oil in aging wells, coal, lignite, peat and tar sands, and in particular to a method and apparatus for extraction of kerogen oil and hydrocarbon gas from oil shale in situ utilizing electrical energy and critical fluids (CF), and extraction of contaminants or residue from a body of fixed earth or from a vessel in situ utilizing electrical energy and critical fluids (CF).
2. Description of Related Art
Oil shale, also known as organic rich marlstone, contains organic matter comprised mainly of an insoluble solid material called kerogen. Kerogen decomposes during pyrolysis into kerogen oil and hydrocarbon gasses, which can be used as fuels or further refined into other transportation fuels or products. Shale oil and hydrocarbon gas can be generated from kerogen by a pyrolysis process, i.e. a treatment that consists of heating oil shale to elevated temperatures, typically 300 to 500° C. Prior to pyrolysis, kerogen products at room temperature have substantial portions of high viscosity non-transformed material such that they cannot be accessed within the rock/sand matrix. The shale oil is then refined into usable marketable products. Early attempts to process bodies of oil shale in situ by heating the kerogen in the oil shale, for example, injecting super-heated steam, hot liquids or other materials into the oil shale formation, have not been economically viable even if fundamentally feasible (which some were not). Early and current attempts to process bodies of oil shale above ground to obtain the kerogen in the oil shale, for example, by mining, crushing and heating the shale in a retort type oven, have not been environmentally feasible nor economically viable.
It is well known to use critical fluids for enhanced oil and gas recovery by injecting naturally occurring carbon dioxide into existing reservoirs in order to maximize the output of oil and gas. By pumping carbon dioxide or air into the reservoirs, the existing oil or gas is displaced, and pushed up to levels where it is more easily extracted.
An article by M. Koel et al. entitled “Using Neoteric Solvents in Oil Shale Studies”, Pure Applied Chemistry, Vol. 73, No. 1, PP 153-159, 2001 discloses that supercritical fluid extraction (SFE) at elevated temperatures with carbon dioxide modified with methanol or water can be used to extract kerogen from ground shale. This study was targeted at replacing analytical techniques using conventional solvents. Most of these solvents are not environmentally desirable and are impractical for use on a large scale.
In a paper by Treday, J. and Smith, J, JAIChE, Vol. 34, No. 4, pp 658-668, supercritical toluene is shown to be effective for the extraction of kerogen from shale. This study used oil shale which was mined, carried to above ground levels, and ground to ¼″ diameter particles in preparation for the extraction. This labor intensive preparation process was to increase diffusivity, as the in-situ diffusivity reported would not support toluene's critical point of 320 degrees Celsius. “In-Situ” diffusivity of 5×10−9 M2/s was estimated, resulting in a penetration of a few centimeters per day which was insufficient. Furthermore the cost of toluene and the potential environmental impact of using toluene in-situ were prohibitive. Finally, maintaining the temperature of 320 degrees Celsius would be expensive in a toluene system.
In a paper by Willey et. al, “Reactivity Investigation of Mixtures of Propane on Nitrous Oxide”, scheduled for publication in December, 2005 in Process Safety Progress, the use of CO2 to inhibit an oxidation reaction from becoming a hazardous runaway reaction is demonstrated. However in this article it is not contemplated to use such a reactant for in-situ fossil fuel processing, shale heating, etc.
Critical fluids are compounds at temperatures and pressures approaching or exceeding the thermodynamic critical point of the compounds. These fluids are characterized by properties between those of gasses and liquids, e.g. diffusivities are much greater than liquids, but not as great as gasses and viscosity is lower than typical liquid viscosities. Density of critical fluids is a strong function of pressure. Density can range from gas to liquid, while the corresponding solvent properties of a critical fluid also vary with temperature and pressure which can be used to advantage in certain circumstances and with certain methods. Critical fluids were first discovered as a laboratory curiosity in the 1870's and have found many commercial uses. Supercritical and critical CO2 have been used for coffee decaffeination, wastewater cleanup and many other applications.
Many efforts have been attempted or proposed to heat large volumes of subsurface formations in situ using electric resistance, gas burner heating, steam injection and electromagnetic energy such as to obtain kerogen oil and gas from oil shale. Resistance type electrical elements have been positioned down a borehole via a power cable to heat the shale via conduction. Electromagnetic energy has been delivered via an antenna or microwave applicator. The antenna is positioned down a borehole via a coaxial cable or waveguide connecting it to a high-frequency power source on the surface. Shale heating is accomplished by radiation and dielectric absorption of the energy contained in the electromagnetic (EM) wave radiated by the antenna or applicator. This is superior to more common resistance heating which relies solely on conduction to transfer the heat. It is superior to steam heating which requires large amounts of water and energy present at the site.
U.S. Pat. No. 3,881,550 issued May 6, 1975 to Charles B. Barry and assigned to Ralph M. Parson Company, discloses a process for in situ recovery of hydrocarbons or heavy oil from tar sand formations by continuously injecting a hot solvent containing relatively large amounts of aromatics into the formations, and alternatively steam and solvents are cyclically and continuously injected into the formation to recover values by gravity drainage. The solvents are injected at a high temperature and consequently lie on top of the oil shale or tar sand and accordingly no complete mixing and dissolving of the heavy oil takes place.
U.S. Pat. No. 4,140,179 issued Feb. 20, 1979 to Raymond Kasevich, et al. and assigned to Raytheon Company discloses a system and method for producing subsurface heating of a formation comprising a plurality of groups of spaced RF energy radiators (dipole antennas) extending down boreholes to oil shale. The antenna elements must be matched to the electrical conditions of the surrounding formations. However, as the formation is heated, the electrical conditions can change whereby the dipole antenna elements may have to be removed and changed due to changes in temperature and content of organic material.
U.S. Pat. No. 4,508,168, issued Apr. 2, 1985 to Vernon L. Heeren and assigned to Raytheon Company, is incorporated herein by reference and describes an RF applicator positioned down a borehole supplied with electromagnetic energy through a coaxial transmission line whose outer conductor terminates in a choking structure comprising an enlarged coaxial stub extending back along the outer conductor. It is desirable that the frequency of an RF transmitter be variable to adjust for different impedances or different formations, and/or the output impedance of an impedance matching circuit be variable so that by means of a standing wave, the proper impedance is reflected through a relatively short transmission line stub and transmission line to the radiating RF applicator down in the formation. However, this approach by itself requires longer application of RF power and more variation in the power level with time. The injection of critical fluids (CF) will reduce the heating dependence, due solely on RF energy, simplifying the RF generation and monitoring equipment and reducing electrical energy consumed. The same is true if simpler electrical resistance heaters are used in place of the RF. Also, the injection of critical fluids (CF) as in the present invention increases the total output of the system, regardless of heat temperature or application method, due to its dilutent and carrier properties.
The process described in U.S. Pat. Nos. 4,140,179 and 4,508,168 and other methods using resistance heaters, require a significant amount of electric power to be generated at the surface to power the process and does not provide an active transport method for removing the products as they are formed and transporting them to the surface facilities. CO2, or another critical fluid, which also acts as an active transport mechanism, can potentially be capped in the shale after the extraction is complete thereby reducing greenhouse gases released to the atmosphere.
U.S. Pat. No. 5,065,819 issued Nov. 19, 1991 to Raymond S. Kasevich and assigned to KAI Technologies discloses an electromagnetic apparatus for in situ heating and recovery of organic and inorganic materials of subsurface formations such as oil shale, tar sands, heavy oil or sulfur. A high power RF generator which operates at either continuous wave or in a pulsed mode, supplies electromagnetic energy over a coaxial transmission line to a downhole collinear array antenna. A coaxial liquid-dielectric impedance transformer located in the wellhead couples the antenna to the RF generator. However, this requires continuous application and monitoring of the RF power source and the in-ground radiating hardware, to provide the necessary heating required for reclamation.